#define _CRT_SECURE_NO_WARNINGS 1

#include <string>
using namespace std;

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode() : val(0), left(nullptr), right(nullptr) {}
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
    TreeNode(int x, TreeNode* left, TreeNode* right) : val(x), left(left), right(right) {}
};

class Solution {
public:
    string tree2str(TreeNode* root) {
        string ret;
        _tree2str(root, ret);
        return ret;
    }
    void _tree2str(TreeNode* root, string& ret)
    {
        if (root == nullptr)
            return;
        ret += to_string(root->val);;
        if (root->right != nullptr || root->left != nullptr)
        {
            ret += '(';
            _tree2str(root->left, ret);
            ret += ')';
        }
        if (root->right != nullptr)
        {
            ret += '(';
            _tree2str(root->right, ret);
            ret += ')';
        }
    }
};